Date: Fri, 02 Nov 2007 16:17:45 -0400
From: Jason Ray
To: Todd R. Hunter
Subject: Re: Accelerometer Calibration
Hi Todd,
Yes, the X axis is setup differently than the Y and Z axes. We set it up to
have a ~0.625V offset for 0 G's, using an op amp with a gain of 10 before
feeding it into the A/D channel.
If memory serves, we set it up this way because the X-axis A/D is only
16-bit and it is single ended. So, we added the 0.625V offset to allow the
signal to swing both directions without saturating the ADC on the low end.
Then we position it parallel to the EL axle so that it sees minimal gravity
effect, regardless of the GBT's elevation angle. If it were positioned
otherwise and had significant gravity effect then it would quickly saturate
the ADC on the high end because of the op amp gain.
As for the uneven scaling, I'll have to set it up on the bench to see if
something's wrong or if I can remember why it does that.
I hope this partially answers your questions. If not, let me know.
Thanks,
Jason
-- ToddHunter - 19 Dec 2007